With a recent demand for a reduction in fuel consumption of automobiles, a conjugated diolefin-based (co)polymer rubber having low rolling resistance, and excellent wear resistance and failure characteristics, and also having steering stability represented by wet-skid resistance has been desired as a rubber material for tires.
In order to reduce the rolling resistance of a tire, the hysteresis loss of vulcanized rubber may be lowered. As indexes for the evaluation of vulcanized rubber, impact resilience at 50 to 80° C., tan δ at 50 to 80° C., Goodrich heat build-up, and the like are used. A rubber material having either high impact resilience at 50 to 80° C., or low tan δ at 50 to 80° C. or low Goodrich heat build-up is preferred.
As a rubber material having low hysteresis loss, natural rubber, polyisoprene rubber, polybutadiene rubber or the like is known. However, they have the problem of low wet-skid resistance.
As for the reducing of the hysteresis loss without impairing the wet-skid resistance, a method was proposed, wherein a functional group was introduced into a terminal of a styrene-butadiene copolymer which was polymerized by use of an organic lithium initiator in a hydrocarbon solvent and had a variety of structure. There are known a styrene-butadiene copolymer obtained by modifying or coupling a terminal of a polymer with a tin compound (Japanese Patent Laid-Open Publication (Sho) 57-55912) and a styrene-butadiene copolymer obtained by modifying a terminal of a polymer with an isocyanate compound or the like (Japanese Patent Laid-Open Publication (Sho) 61-141741). These modified polymers exert the effects of reducing the hysteresis loss without impairing the wet-skid resistance and providing excellent wear resistance and failure characteristics, particularly in a composition comprising carbon black as a reinforcing agent.
On the other hand, there has recently been proposed a method of using as a rubber material for tires a rubber composition comprising silica or a mixture of silica and carbon black as a reinforcing agent. A tire tread comprising silica or a mixture of silica and carbon black has low rolling resistance and excellent steering stability represented by wet-skid resistance. On the other hand, the tire tread has the problem that the tensile strength and wear resistance of a vulcanizate are low. The above-mentioned modified styrene-butadiene copolymer becomes a rubber material for tires having excellent wear resistance and failure characteristics in the composition using carbon black as the reinforcing agent. However, in the composition using silica as the reinforcing agent, the improving effect thereof is small.
In order to improve the tensile strength and wear resistance of the vulcanizate comprising silica or a mixture of silica and carbon black as the reinforcing agent, rubber compositions each containing a polymer into which a functional group having an affinity for silica is introduced have been proposed. Japanese Patent Examined Publication (Sho) 49-36957 proposes a method of reacting a silicon tetrahalide, a trihalosilane, etc. to produce a polymer. Further, Japanese Patent Examined Publication (Sho) 52-5071 discloses a method for producing a polymer modified with a silane halide compound. Furthermore, Japanese Patent Laid-Open Publication (Hei) 1-188501 discloses an alkylsilyl group-introduced diene-based rubber, and Japanese Patent Laid-Open Publication (Hei) 5-230286 discloses a silyl halide group-introduced diene-based rubber. In addition, Japanese Patent Laid-Open Publication (Hei) 7-233217 discloses a diene-based rubber into which a tertiary amino group and an alkoxysilyl group is introduced.
The physical properties are improved to a certain degree by using each of these modified polymers in the composition comprising silica or a mixture of silica and carbon black. However, the tensile strength and wear resistance of the vulcanizate are not sufficiently improved yet. In particular, when a mixture of silica and carbon black is incorporated, a reduction in hysteresis loss is also insufficient with an increase in the ratio of carbon black. Further, in general, a silica-containing composition is inferior in processability to a carbon black-containing composition, which poses the problem of high processing cost. When the above-mentioned polymer into which a functional group having an affinity for silica is introduced is used, the processability thereof is unfavorably apt to deteriorate.
Modified polymers which have hitherto been known are mainly classified into two types, polymers suitable for carbon black mixing and polymers suitable for silica mixing. When the kind of reinforcing agent is changed in producing a tire etc., it has been necessary to select a rubber to be used again. Further, when a mixture of silica and carbon black is contained, even the use of either of the types of modified polymers has increased or decreased the effect thereof in correlation with the mixing ratio of silica to carbon black.
In both the carbon black mixing and the silica mixing, amino group-introduce polymers are conceivable as effective modified polymers. For the carbon black mixing, there are proposed (1) polymers each having an amino group introduced into a polymerization terminal by use of a lithium amide initiator (refer to Japanese Patent Laid-Open Publication (Sho) 59-38209, Japanese Patent Examined Publication (Hei) 5-1298, Japanese Patent Laid-Open Publication (Hei) 6-279515, Japanese Patent Laid-Open Publication (Hei) 6-199923 and Japanese Patent Laid-Open Publication (Hei) 7-53616) and (2) polymers each obtained by modifying a polymer terminal of a styrene-butadiene copolymer which is polymerized by use of an organic lithium initiator and has a variety of structure with a nitrogen-containing compound such as a urea compound (refer to Japanese Patent Laid-Open Publication (Sho) 61-27338), a dialkyl aminobenzophenone compound (refer to Japanese Patent Laid-Open Publication (Sho) 58-162604 and Japanese Patent Laid-Open Publication (Sho) 58-189203) or a lactam compound (Japanese Patent Laid-Open Publication (Sho) 61-43402). Further, as polymers for silica mixing, amino group-introduced diene-based rubbers are proposed in Japanese Patent Laid-Open Publication (Hei) 1-101344, Japanese Patent Laid-Open Publication (Sho) 64-22940 and Japanese Patent Laid-Open Publication (Hei) 9-71687.
The polymers obtained by these methods have achieved the improvements of various characteristics to a certain degree. However, the above-mentioned literatures mainly describe in detail the methods for introducing amino groups into the polymers, but make reference to nothing more than general matters with respect to the relationship between the structure of the polymer itself and each performance.
Further, these diene-based rubbers into which amino groups etc. are introduced also have high cold flow properties in some cases, and have trouble with storage stability etc., thus practically having problems.
Furthermore, there is generally known a method of polymerizing a conjugated diolefin alone or an aromatic vinyl compound therewith in the presence of an anionic polymerization initiator, and coupling the resulting living polymer using a silicon halide compound such as tetrachlorosilane as a coupling agent to produce a branched conjugated diolefin (co)polymer rubber useful for automobile tires etc. However, such a coupling agent contains a halogen atom as a reactive site, and produces a halogen-containing compound such as LiCl as a by-product after the coupling reaction. On the other hand, it has been desired that a halide existing in a rubber is reduced.
For this purpose, various coupling agents of the non-halogen family have been proposed. For example, there is proposed a method for producing a conjugated diene-based polymer having a specific branched structure, using an alkoxysilane as the coupling agent (Japanese Patent Laid-Open Publication (Hei) 7-2958).
However, when the alkoxysilane is used as the coupling agent, the resulting branched conjugated diolefin (co)polymer rubber has the problem not observed in the coupling reaction with a conventional polysilicon halide compound that a polymer component having a structure other than a desired branched structure is formed with an elapse of time.
In order to solve this problem, Japanese Patent Laid-Open Publication (Hei) 10-25313 proposes a method of polymerizing a conjugated diene-based monomer using an organic lithium compound as an initiator in a hydrocarbon solvent to produce a living polymer, and coupling it using an alkoxysilane compound, followed by treatment by addition of at least one kind of Lewis base selected from a tertiary diamine, a chain ether having two or more oxygen atoms in one molecule or a cyclic ether to the above-mentioned hydrocarbon solvent, as a method for producing a halogen-free branched conjugated diene-based polymer effectively and stably.
However, also in this method, the Mooney viscosity of the resulting polymer is not stabilized, and it is difficult to restrain the change in the Mooney viscosity of the polymer with an elapse of time.
In recent years, needs for granular rubber chemical masterbatches etc. in the market have become strong from the following background.
(a) From the aspect of the working environment in workplaces, scattering of fine powdery rubber chemicals etc. is prevented.
(b) Rubber chemicals to be added to rubber compositions can be mixed for a short period of time, and are excellent in dispersibility in the compositions.
(c) It is possible to automatically measure the rubber compositions.
In order to solve the above (a) and (b), for example, sheet-like rubber chemical masterbatches using usual rubbers and rubber chemicals treated with oil have hitherto been known. However, from the automatic metering of the rubber chemicals and handling advantages, demands for granular chemical masterbatches have recently been increased.
As technology relating to the rubber chemical masterbatch, Japanese Patent Laid-Open Publication (Hei) 1-223130 proposes a rubber compounding agent composition comprising three components of a rubber chemicals, a rubber and an ethylene-vinyl acetate copolymer, and an oil. However, depending on the type of the rubber chemicals or the composition ratio of three components, the composition has adhesion, and has a problem with regard to processing or storage of the composition. For example, when a sheet-like masterbatch is produced, sheeting is performed with rolls. In this case, when the adhesion of the composition is high, the sheet adheres to the rolls, resulting in poor release properties, which causes significantly impaired workability in some cases. Further, a mixed composition as described above is formed by granulation with an extrusion granulator in some cases, in order to rationalize the metering. When the adhesion of the composition is high, granules adhere to one another by their own weight (blocking) during storage of a granulated product to form a block, thereby impairing their function in some cases. In particular, this tendency is significant in storage at a summer season when the outdoor air temperature is elevated.
On the other hand, Japanese Patent Laid-Open Publication (Sho) 53-41342 describes that a rubber is selected as a binder and a process oil for rubber is selected as an oil in producing a masterbatch according to a composition comprising the rubber, a vulcanization accelerator, etc. However, this masterbatch has the problem of the adhesion of itself, and has the problem of the above-mentioned blocking.
In order to solve the above-mentioned problems, Japanese Patent Laid-Open Publication (Hei) 7-224188 proposes a rubber-plastic chemical masterbatch comprising (a) rubber-plastic chemicals, (b) 1,2-polybutadiene and (c) a softening agent as indispensable components, maintaining a good shape which is the intended purpose of the masterbatch, further preventing the adhesion of a composition without impairing good dispersibility in a rubber, a elastomer or a plastic, and improving roll processability or blocking properties during storage. However, this masterbatch has insufficient fluidity, insufficient dispersibility of various chemicals, and it is difficult to disperse the chemicals in the masterbatch in large amount. Further, a technique is required for preparing the masterbatch, and the preparation takes a long period of time.
Additionally, the technical idea that an affinity for an inorganic filler is intended by giving a specific functional group to a rubber component itself used in a masterbatch is not found in the above-mentioned prior art.
An object of the present invention is to provide a conjugated diolefin (co)polymer rubber having good processability in both carbon black mixing and silica mixing, and usable as a material for a tread of a tire for low fuel consumption, a large sized tire or a high performance tire in which low hysteresis loss properties and wet-skid characteristics are improved at the same time without impairing wear resistance and failure characteristics, or low hysteresis loss properties, wear resistance and failure characteristics are improved at the same time in a balanced manner without impairing wet-skid characteristics; a process for producing the same; a rubber composition; and a tire.
Another object of the present invention is to provide a conjugated diolefin (co)polymer rubber further improved also in cold flow properties; a process for producing the same, etc.
Still another object of the present invention is to provide a conjugated diolefin (co)polymer rubber in which the conjugated diolefin (co)polymer rubber having alkoxysilyl groups bound to a (co)polymer chain can be stably produced with respect to Mooney viscosity, and the subsequent variation in Mooney viscosity with the elapse of time can also be restrained; a process for producing the same; etc.
A further object of the present invention is to provide a rubber-inorganic compound composite giving a high-performance masterbatch in which a rubber chemical, particularly an inorganic compound, can be dispersed uniformly and in large amounts, using a novel conjugated diolefin (co)polymer rubber having a specific functional group and an affinity for an inorganic compound (inorganic filler), and which can be easily prepared by ordinary rubber kneading technology. A still further object of the present invention is to provide a masterbatch having more excellent characteristics by uniform dispersion of an inorganic compound.